A standard filter press has a plurality of compartments defined between filter plates and each subdivided by a filter cloth or screen into an input compartment and an output compartment. The filter plates have ridged and grooved front surfaces turned toward the filter cloth and forming drainage channels in the respective output compartments. The filtrate is introduced into the input compartment and the liquid phase is extracted along the channels from the output compartment, with the solid phase of the suspension left on the filter cloth.
As described in commonly owned U.S. Pat. No. 4,997,560, in order to clean such a filter the center panels of the filter plates are constituted as membranes that are sufficiently elastic or resilient that the plates of each compartment can be pushed toward each other to press the solid phase on the two filter cloths into a filter cake that can be back flushed or otherwise emptied from the machine. This forward deflection to compress the solid phase is effected by pneumatically or hydraulically pressurizing another compartment formed between the back face of the plate and a relatively rigid backing plate located immediately behind each filter plate.
PCT patent application PCT/EP91/01584 based on German 4,118,620 filed 6 Jun. 1991 by H. Bonn describes such a system where each membrane plate has a thickened outer edge or frame that sits in a groove of the rigid backing or support plate. An annular clip sits on each frame to retain it in place in the groove. This clip is a complex two-part item that must be perfectly set in order for the filter to function, in particular because the drain passages in part pass through the clip.